Uninterruptable Wifi Supply

September 16, 2009 4:41 PM

What's a good, small and basic UPS for just backing up up my T-mobile VOIP/wifi router device and possibly a cable modem?

My family recently decided to switch from Comcast Digital Voice and AT&T cell phones to T-mobile's @home service. Our home gets almost no cell phone reception, so it's nice that the router (a Linksys WRTU54G) allows us to make VOIP calls over both the wired phones and our cell phones. However, this means that our calling is basically coming down to just one electronic box, with only a sketchy 1-bar cellular connection in the event we lose power. The max DC draw of the antenna is 1.5 A at 12 volts, but it's probably much less in practice. I don't have anything to measure it, though.

Realizing this, I think it's important we get a UPS that can keep our router online for 6 hours to a day. Our modem comes with its own 12 hour battery, because it used to be the VOIP hardware for our Comcast VOIP service, so I could keep it off of the UPS to save power, although Comcast is liable to take it back. In my dream product, this UPS could also charge from a car's 12V socket in the event of a very long power outage, but we've never had a long one over a few minutes in our relatively new (~20 years old) NJ suburb.

I really don't want or need the UPS to keep our desktop computer up and running. I have a laptop, and my mom and sister know to save as they go along when working on a desktop. What I really need is something inexpensive and reliable so that we can still call 911 in the event of a power outage. Preferably, the solution doesn't end up being something too bulky or hacky (ie "Just wire up some car batteries in parallel!").

posted by mccarty.tim to technology (8 comments total)

Hell no, you shouldn't wire up car batteries in parallel! Instead, you should use deep-cycle marine batteries.

Seriously, any UPS should be able to do what you want. A 600-750 VA unit will power a draw of about 1 amp for about 6 hours. I recommend APC. And no, I don't think the router will draw the full 1.5 amps either.

The reason people are going to suggest car batteries is that the device you want to provide backup power for is DC powered (at 12V no less!), so a traditional UPS (that goes from AC to DC to charge the battery, and back to AC again when running on battery, only to go back to DC in the router's wall-wart) is kind of going the long way 'round and will lose lots of power. A single, smallish marine battery is going to easily power that router for a whole day and cost you much less than a UPS with equivalent runtime. A sealed lead-acid (SLA) cell like the one used in a UPS would cost like $25 and would run the router for twice what a UPS using the battery would.
posted by kindall at 5:37 PM on September 16

1500kva APC UPS or maybe as small as a 600/900KVA APC UPS.

If you're worried about extended power outages buy a gasoline powered generator...
posted by iamabot at 5:40 PM on September 16

Whichever one you chose, beware the beeper!
posted by Marky at 6:39 PM on September 16

Honestly, I'm not too concerned about this. If I can get something decent that will work for 6 hours at $20-50, I'll do that.

I'm a bit intrigued at using a battery directly wired to the router, if it's not too hard to set it up. Does this require soldering? I probably won't do it. I just like reading about how to hack things together even though I rarely follow through.
posted by mccarty.tim at 7:12 PM on September 16

Get a nice car battery charger and 12v sla (sealed lead acid - deep cycle) battery, maybe run your cabling so that you have to plug the battery into the router (so you will lose power for a minute, but you don't have to worry about feeding 13.8v (or whatever) into your router when the battery is charging). One question though, do you know if the modem you are plugged into on the other end is powered for any reasonable length of time? Traditional phone has requirements that there is battery backup for the phones for x hours (hence your wired phone keeps working with a traditional phone line), but I'm not sure equivalent requirements exist for the IP infrastructure to your house, so if the exchange box loses power - your internet drops out. Somebody around here can hopefully give a better answer.
posted by defcom1 at 10:01 PM on September 16

Oh and to answer your second question, it's not hard at all to run the battery directly into the router. grab a cheap universal power adaptor or find some other source for a barrel plug which fits into the back of your router. The power adapter for your router will have a symbol on it telling you which bit of the barrel plug is positive and negative (pin positive / outside negative or the other way 'round). Simply run a wire from the corresponding terminal on the battery to the right place on the barrel plug. Plug your new barrel plug wired to the battery in to the modem. Hold the whole mess together with some electrical tape and zip ties for the true MacGyver feel.
posted by defcom1 at 10:08 PM on September 16

Thanks for your help, everyone. I guess I was mostly just hoping somebody sold a 12V wall wart with a built-in backup battery, but I guess that product doesn't exist. I don't feel like kludging something together, though, so I might just search for a cheap USPs that's good enough for keeping my router up.

If I were a braver guy who owned my own battery-backed up modem, I'd open up the one I'm renting from Comcast, and wire power over Ethernet from it's power supply to my router. That'd be ideal.
posted by mccarty.tim at 8:24 AM on September 17

Yeah, POE from the modem would be sweet! I may steal that idea sometime.
posted by kindall at 4:45 PM on September 17